Mask



FIG. 1 is a front view of a mask showing my new design;

FIG. 2 is a back view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof.

The broken lines in the drawings illustrate portions of the mask that form no part of the claimed design. 

CLAIM The ornamental design for a mask design as shown and described. 